Near field patterns have almost nothing to do with far field patterns, so
that would be a great deal of walking and require a pretty sensitive
instrument. To be in the area where the pattern is reasonably formed, a
person would have to be at least a wavelength and at least 5-10 times the
physical area of the antenna away from the antenna, whichever is greatest.
For example, my transmitting four square on 160 has not reasonably formed a
consistent pattern until I am out about 2500 feet. A small loop stabilizes
at about a wavelength.
I'd expect the BOG to approach the distance of the four square.
There are two reasons for this. One is the induction fields have not been
fully dominated by the radiation field until near a wavelength for a very
small antenna. The other reason is to form the pattern, the sense antenna
and measured antenna have to be so far apart that all radiating areas of
each antenna appear to originate from a single point in space.
If it doesn't look almost like a single point for both the sense and main
antennas, the pattern won't be the actual pattern.
The way you get around this is to add a dielectric sheath in the model, like
wire insulation, that slows the wave like ground would. Then, if you match
the current levels and phase, you will pretty much get the correct pattern.
When I was working with slow wave antennas, I measured phase shift and
currents and adjusted the model to match the antenna. If you do that, it
doesn't matter if the wire is above earth in the model. It comes out a close
match.
Otherwise, be prepared to drive a few miles while confirming pattern. :)
----- Original Message -----
From: "K1FZ-Bruce" <k1fz@myfairpoint.net>
To: "Topband" <topband@contesting.com>
Sent: Wednesday, June 17, 2015 10:15 AM
Subject: Topband: RX antenna pattern
BOG antennas are difficult to model. Programs do not like wires on/under
ground.. It is possible to find actual BOG, and Beverage patterns at
ground level.
Feed a few watts of RF signal into the BOG/Beverage antenna. Use a
portable SW receiver with S meter to walk around the antenna to take
measurements and plot.
Hope you have friendly neighbors !
73
Bruce-K1FZ
www.qsl.net/k1fz/bogantennanotes/index.html
www.qsl.net/k1fz/beverage_antenna.html
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